Effect Of Liquid Flow Rate Research Articles

Droplet size measurements in horizontal annular gas–liquid flow

Measurements of drop size distributions in air–water annular flow have been made in a horizontal 0.0953 m pipe, at atmospheric pressure. A laser diffraction technique has been employed, using a Malvern Spraytec R5008 instrument. Stratification of the droplets has been observed by obtaining measurements at the pipe centre line, and 0.019 m above and below it. The stratification, which is caused by the effects of gravitational settling and the asymmetry of the liquid film, decreases with increasing gas velocity. Measured Sauter mean diameters at the pipe centre are similar to what has been observed in vertical pipes. However, they show a stronger effect of liquid flow rate than predicted by the correlation of Azzopardi, that was developed from measurements made with an earlier diffraction technique that did not account for multiple scattering. A log-normal or an upper limit log-normal distribution underpredicts the measured contributions of small diameter drops.

Transient processes in a closed vessel due to injection of hot liquid sprays

An experimental and theoretical study has been made to investigate the transient processes which occur when hot liquid spray droplets are suddenly injected into a gas contained in a closed chamber. A novel experimental apparatus was employed in which hot water is injected via commercial solid cone spray nozzles into air enclosed in a cylindrical spray chamber, of 121 mm diameter and 190 mm height, at a pre-determined constant flowrate, and for a set duration, under computer control. Measurements were made of the spray chamber pressure rise with time due to the combined effects of liquid—gas heat transfer, droplet evaporation and liquid accumulation in the chamber. The experimental results reported in the paper cover a range of nozzle sizes, in both single-nozzle and multi-nozzle configurations, and the effects of liquid flowrate, initial gas pressure and initial liquid—gas temperature difference are considered. A simple analytical model has been developed which subdivides the chamber volume into three zones: a liquid zone, a transfer zone where heat and mass transfer occurs, defined by the spray cone angle, and a still zone outside the spray cone. The analysis gathers the important parameters governing droplet heat transfer in a single dimensionless group, denoted by K2. For the range of conditions investigated, reasonable agreement between the experimental results and the theoretical solutions were obtained with a value of K2 = 2 × 10−5.

Filtration of biomass with axial inter-fibre upward slug flow: performance and mechanisms

This paper describes the performance and mechanisms of filtration of biomass with vertical inter-fibre two-phase flow. The effect of bubbling on particle deposition on hollow fibre membranes was studied in a specially designed cross-flow cell in which the fibres were arranged with well-controlled spacing such that slug flow could form between fibres. The enhancement of performance by bubbling and the effect of liquid flow rate, gas flow rate, and fibre orientation on filtration performance were investigated. The difference in flux between operation with pump recirculation and airlift systems was also assessed. The results show that bubbling is effective in enhancement of the filtration performance but the enhancement is not sensitive to changes in two-phase flow mixture velocity when the operation is controlled by the deposition in the falling film zone induced by slugs. A theoretical slug-flow mode is developed to illustrate the insensitivity of falling film velocity on mixture velocity. The experiments demonstrate that the axial vertical fibre orientation is superior to transversal orientation for two-phase flow filtration and a higher flux can be achieved with pumped circulation rather than with the airlift system because pumping liquid through the cell can result in a more stable and regular slug flow.

Kinetics of solvent extraction in hollow-fiber contactors

Kinetics of membrane-based extraction can be controlled by the boundary layers and/or by the membrane transfer resistance, depending on the flow configuration and the nature of the membrane. While the mass transfer coefficients on a tube side of hollow-fiber contactors are well defined, there is a need to establish a suitable correlation to predict the coefficients on a shell side. Using several commercial hollow-fiber modules the extraction of ethanol from aqueous solution into n-octanol has been investigated experimentally. The effect of liquid flow rates, membrane type and packing density of modules on the extraction kinetics has been studied. Experimental results have been correlated by a new dimensionless equation for the shell side mass transfer, valid for low Reynolds numbers and high packing densities.

A multivariate study of the acid effect and the selection of internal standards for inductively coupled plasma mass spectrometry

The effects of nitric acid concentration and liquid flow rate on the signals obtained with an inductively coupled plasma mass spectrometer, operated with a microconcentric nebulizer (MCN-100), have been studied by the use of partial least squares regression. Thirteen elements, covering the mass range 51–238, were studied. The nitric acid concentration was varied in the range 0.14–2.8 mol l −1 and the acid effect was found to vary significantly between the elements — depending mainly on the value of the first ionisation potential of the element. The effect of the liquid flow rate was studied within the range 34.5–172.5 μl min −1 and it was only significant ( P=0.05) for 107Ag and 109Ag. It is possible to compensate completely for the acid matrix effect by the use of a proper internal standard. The use of multivariate analysis methods, e.g. partial least squares regression is recommended in order to choose the most suitable internal standards.

Hydrogenation of crotonaldehyde under periodic flow interruption in a trickle bed

The conversion and consumption rate of crotonaldehyde under steady operation (constant liquid flow) and periodic operation (on–off liquid flow) at 25°C and 1.1 MPa pressure were compared at equal time-average liquid flow rates. Steady experiments showed the effect of liquid flow rate on conversion and consumption and also provided kinetic data. Liquid flow rates were varied over approximately two orders of magnitude. Periodic experiments involved studies of the effect of period length, period split and flush amplitude on time-average conversion and consumption rate. The periodic operation data were compared with steady operation data on a time-average liquid flow rate basis. The comparison showed that for higher liquid flow rates both conversions and rates of consumption under periodic operation were less than those under comparable steady operation. However for lower liquid flow rates (0.04–0.4 kg/(m 2 s)), the opposite occurred, with periodic operation showing up to 50% increase in the crotonaldehyde consumption rate.

Harmonic spraying of conducting liquids employing AC-DC electric fields

This paper reports the results of the work carried out to investigate the breakup process of charged conducting liquid jet under the influence of an AC field superimposed onto a DC field. The main aim of this paper is to optimize the spraying parameters and to generate uniform droplets of highly conducting liquid in a controlled fashion by varying the strength and the frequency of the applied AC field. The electric field at the tip of a blunt needle facing a ground electrode was examined using a finite-element modeling technique. Three types of ground electrode configurations were investigated. A mathematical model for the electrostatic force on the leading edge of the droplet as a function of the liquid flowrate, the applied voltage, and distance between the capillary tip and the ground electrode has been developed. The breakup and droplet formation processes were investigated using a telemicroscopic lens and charge-coupled device (CCD) camera. The video data was processed using frame grabber software installed on a PC. The digital images were then analyzed utilizing image analysis software to give information on the breakup process and the size of droplets. A frequency range was identified where the formation of the droplets was synchronized with the applied AC field frequency. The effects of liquid flowrate on the synchronous bands were examined. The experimental results showed the dependency of the droplets size and the emission frequency on the applied AC frequency.

Nonwetting flow of a liquid through a packed bed with gas cross-flow

In this study, the effect of a cross-flow gas field on the percolating flow of a non-wetting liquid through a packed bed was investigated. Experiments were conducted to measure the liquid shift, due to the cross-flow of air, for the flow of aqueous barium chloride solutions and mercury percolating through beds of polyethylene and expanded polystyrene particles. An X-ray technique was used to visualize the liquid flow pattern through the packed bed. The liquid percolates through a packed bed as a series of rivulets and droplets which are continuously breaking up and coalescing. A mathematical model to predict the direction of the liquid rivulet/droplet flow under the influence of a gas flow field was developed. The model treats the liquid as a discrete phase and includes the effects of gravity, gas drag, and inertial and viscous bed resistance. The effective droplet/rivulet size is an important model parameter, and the model postulates that the droplet/rivulet size is a function of both the effective capillary size of the bed and the liquid flow rate. A simplified population balance analysis for droplet coalescence is used to predict the effect of liquid flow rate on droplet/rivulet size. The model predictions are consistent with the experiments.

Monodisperse Electrosprays of Low Electric Conductivity Liquids in the Cone-Jet Mode

An experimental investigation was performed on electrosprays of low electric conductivity liquids (heptane with different amounts of an antistatic additive) that were operated in the cone-jet mode. The effects of liquid flow rate, applied voltage, and liquid electric conductivity on droplet size and spray monodispersity were systematically investigated. The droplet size was found to be dominantly controlled by the liquid flow rate and secondarily by the applied voltage. It showed no dependence on capillary size. For a given liquid, stable and monodisperse electrosprays could be established only within certain ranges of liquid flow rates and applied voltages, that defined a cone-jet domain. This domain was affected by the electric conductivity of the liquid. As the liquid electric conductivity increased, the domain shifted toward smaller flow rates which implies that smaller droplets were generated in the spray. An increase in the capillary diameter caused a narrowing of this domain. Outside the cone-jet domain, electrosprays were unstable and polydisperse with different instability patterns that depended on the applied voltage and the liquid flow rate. Experiments also showed that the droplet size and the spray monodispersity were independent of the electrode configuration, as long as the electrospray was operated at the onset voltage condition, that is defined as the minimum voltage at which the cone-jet mode was established. By using dimensional analysis the controlling variables were combined into a few dimensionless groups and an empirical fit was derived and was shown to correlate well all the experimental data.

高粘性液体の均一粒のノズル衝撃法による生成

Although a technique for production of uniform size droplets from a large viscosity liquid is required in industrial field, conventional methods are available for only low viscosity liquid. This work has been done to develop and investigate a new method for easy production of high viscous uniform droplets. In the method, impingement of nozzle by cam mechanism on a stopper with adjustable gap imposes cyclic shocks on high viscous liquid jet. Using a silicone oil with viscosity of 10000mPa ·s, the effects of liquid flow rate, diameter of nozzle and intensity of shocks on producible range of the uniform droplets were examined. Although the flow rate was in relatively low range, following results were obtained: uniform size droplets were obtained with fairly good uniformity, the maximum fre-quency in producible conditions for uniform droplets increased with icrease of liquid flow rate, and the droplet sizes obtained were kept some constant values independently of the change of velocity of the liquid flow, according to the change of the diameter of nozzle and the amplitude of imposed frequency.

Modeling of immobilized cell reactor for propionic acid fermentation

A mathematical model of steady state reactor behavior was developed, combining the tanks-in-series model with fermentation kinetic description. The model was tested with experimental data-from an immobilized cell reactor for propionic acid production operated under different residence times. In order to determine the effects of liquid flow rate and gas evolution on the degree of mixing, residence time distribution studies (RTDs) were performed during fermentation. The tanks-in-series model represented adequately the hydrodynamic behavior of the reactor. Association of an intrinsic kinetic model obtained from chemostat studies with the tanks-in-series model allows a "chemostat equivalent" cell concentration profile and a substrate consumption profile to be obtained. The advantage of having a two-level pH adjustment within the reactor is also discussed.

Effect of Liquid Flow Rate on Film Boiling Heat Transfer during Reflood in Rod Bundle

An experiment was performed in a wide range of core flooding rate to study the effect of liquid flow rate on the film boiling heat transfer during reflood using a 6 × 6 heater rod bundle with a full-height heated length. The flooding rate was in the range of 2–30cm/s. The obtained data were evaluated through assessment and improvement of Murao-Sugimoto heat transfer coefficient correlation, which predicted well the heat transfer coefficient under the core flooding rate up to 10 cm/s, but underestimated the heat transfer coefficient in the range of the flooding rate higher than 10 cm/s. An empirical correction factor for the Murao-Sugimoto correlation was proposed based on the present experimental data. The proposed correction factor was confirmed to be applicable to another large scale tests.

Effect of liquid flow rate on film boiling heat transfer during reflood in rod bundle.

An experiment was performed in a wide range of core flooding rate to study the effect of liquid flow rate on the film boiling heat transfer during reflood using a 6 × 6 heater rod bundle with a full-height heated length. The flooding rate was in the range of 2–30cm/s. The obtained data were evaluated through assessment and improvement of Murao-Sugimoto heat transfer coefficient correlation, which predicted well the heat transfer coefficient under the core flooding rate up to 10 cm/s, but underestimated the heat transfer coefficient in the range of the flooding rate higher than 10 cm/s. An empirical correction factor for the Murao-Sugimoto correlation was proposed based on the present experimental data. The proposed correction factor was confirmed to be applicable to another large scale tests.

Mathematical modelling of heat and mass transfer in three phase fluidized bed systems

For absorption and desorption processes, spray columns and packed beds are used in industries. However, they have drawbacks such as low heat and mass transfer rates, large carryover, etc. Fluidized bed systems are found to be efficient and the above problems do not exist. In the present work a mathematical model has been developed to predict the heat and mass transfer in three phase fluidized bed systems, which can be applied for dehumidification of air, cooling of water, gas purification, etc. A finite difference scheme with Crank-Nicholson method has been used to solve the equations. The effect of liquid flow rate and the gas flow rate on Nusselt Number and Sherwood Number are predicted. The variation of residence time is also studied. The results of the localised particle model are extended to the bed model and the overall performance characteristics are also predicted.

Liquid residence time distributions in immobilized cell bioreactors

Previous work has demonstrated that high ethanol productivities can be achieved using yeast or bacterial cells adsorbed onto the surface of ion exchange resin in vertical packed bed bioreactors. The present work quantitatively characterizes the overall degree of backmixing in such reactors at two scales of operation: 2.0 and 8.0 L. Stimulus-response experiments, using two solvents (2,3-butanediol and 2-ethoxyethanol) as tracers, were performed to measure the liquid phase residence time distribution (RTD) during continuous ethanol fermentations using the yeast Saccharomyces cerevisiae and the bacterium Zymomonas mobilis at the 2-L scale, and with S. cerevisiae at the 8-L scale. In order to separately determine the effects of liquid flow rate and gas evolution on the degree of mixing, stimulus-response experiments were also performed in the systems without microbial cells present. The evolution of CO(2) was found to dramatically increase the extent of mixing; however, the tanks-in-series model for non-ideal flow represented the systems adequately. The packed beds were equivalent to over 70 tanks-in-series during abiotic operation while during fermentations, with similar liquid flow rates, they ranged in equivalence from 35 to 15 tanks-in-series. This increased knowledge of the overall degree of mixing in packed bed, immobilized cell bioreactors will allow for more accurate kinetic modelling and efficient scale up of the process.

Heat and mass transfer in wetted-wall columns: I

Mass and heat transfer data are reported for humidification of air in a 4.04 cm diameter glass wetted-wall column with height varied between 0.723 m an Data were shown to vary with gas Reynolds number relative to the liquid film. There was a minor effect of liquid flow rate but no height effect was obs Heat transfer data were reported for the adiabatic operation as there was an effect of inlet gas temperature. No end effect was observed under these co

Flow characteristics of condensate on a vertical column of horizontal low finned tubes.

Experiments were performed to study the flow characteristics of condensate on a simulated bank of horizontal low finned tubes. Two or three tubes arranged in a vertical column were set in a stationary vapor. The top tube had a longitudinal slit at the upper end through which the test liquid was fed uniformly on the tube surface. Cooling water was passed through the lower tubes. The test fluids used were R-113, methanol and normal propanol. Four major flow modes: droplet, column, column-sheet and sheet, were observed as the liquid flow rate was increased. Experimental data on the number of instantaneous falling sites, the proportion of surface area covered with the falling liquid and the flooding angle below which the inter-fin sp. ace was flooded with condensate were obtained for a range of liquid flow rates. Theoretical considerations were given to the effect of liquid flow rate on the flow mode transition and on the measured quantities.

Gas holdup and axial dispersion in gas-liquid concurrent bubble column.

An experimental investigation was carried out to determine the effect of liquid flow on gas holdup and axial dispersion coefficient in a gas-liquid concurrent bubble column 20 cm in diameter, in the ranges of gas and liquid superficial velocities of 0.21-0.87 and 0-1.16ms-1, respectively. Theoretical expressions of the turbulent recirculation flow were developed to account for the effect of liquid flow rate. With increasing liquid upflovv rate, the value of axial dispersion coefficient decreases at relatively small liquid flow rate and turns to increase at large flow rate, whereas the value of gas holdup decreases simply. These phenomena were quantitatively explained by the developed theory, including the effect of column diameter.

The effect of liquid flow rate on flooding in vertical annular countercurrent two-phase flow

The effect of liquid flow rate on flooding in vertical annular countercurrent two-phase flow

THE BEHAVIOR OF THE DISPERSED PHASE IN LIQUID-LIQUID EXTRACTION IN FLUIDIZED BEDS

An investigation was carried out on the effects of liquid flow rates, solid particle size, bed height, and voidage on the dispersed-phase holdup, the drop size and the behavior of the dispersed phase in liquid-liquid concurrent fluidized beds. The mass transfer coefficients were calculated from liquid-liquid extraction data and the calculated results could be satisfactorily explained by matching with the dynamic behavior of the liquids and the change of drop size. The increase of liquid-liquid extraction rates in liquid-liquid fluidized beds was mainly due to the increase of interfacial areas of the dispersed phase.